GPU architecture is a little bit more complex than that, there’s much more happening under the hood than a pointer sharing (access synchronization is just a small part of it), so actually they can often cost you more…
Temporal re-projection will be artefacts hell on fast head movements, so before you think about that, I would personally look at optimizing your scene first, achieving 90 fps twice full hd is not a big deal with a reasonably good graphics card nowadays, so time to optimize patches and post processors ;)
In a non particular order (and non exhaustive):
- Cull as much as you can (high poly geometry)
- Instance as much as you can (low to medium poly geometry)
- Cull instances (medium poly geometry)
- Maximize depth early rejection (eg: your draw order is important).
- Take care of texture formats (fp32 are generally expensive, specially the 4 channels flavour)
- Take care or samplers in post processing (most times you can use point, or no sample at all an just use Load).
- Use stencil maps to optimize post processors (most basic optimization in the world).
- Optimize constant/structured buffers in forward shaders to match frequency of updates.
- Profile your code, if you are badly cpu bound temporal re-projection will not help you ;)